1. Field of the Invention
This invention relates to a valve for controlling fluid flow in a well conduit, and particularly to a so-called lubricator valve commonly utilized for installation of tools in an oil or gas well on a wireline while controlling fluids therethrough.
2. Description of the Prior Art
During the completion, testing or workover of a subterranean well at an inland location, it may be necessary to run equipment such as a perforating gun or the like on a wire or electric line into the well when the well is under pressure. This is achieved by inserting the equipment into a length of production tubing above a Christmas tree, the length of tubing being commonly referred to as a "lubricator riser". The lubricator riser section is isolated from the portion of the well therebelow by one or a series of readily accessible valves. On some inland locations, it may be necessary to extend the lubricator section as high as sixty feet into the air.
On floating locations, where space is at a premium and valves are not readily accessible, an inland type lubricator is not practical. For example, use of such an extended length of tubing may be hazardous when applied to an offshore well site utilizing a floating vessel thereabove. Relative motion between the floating vessel and the tubing string, which is anchored within the well within the sea bed, causes considerable difficulty in the manipulation of manual valves.
Most offshore locations will utilize a riser pipe extending from the floating vessel to the ocean floor where it is connected to the uppermost portion of the drilling blowout preventer stack. The riser functions as casing and provides a conduit for mud circulation and isolation of the well from the sea. Whenever the well is "alive" or capable of flowing, there is usually tubing between the floating vessel and the blowout preventer stack. This tubing will lie inside the riser, if a riser is used. This tubing section is available for use as a lubricator section for insertion therethrough of wire or electric line equipment if a valve is provided therebelow. Use of the riser pipe as a lubricator section will eliminate use of a lubricator riser section extending above the floating vessel and will thereby eliminate the hazards involved in such use.
In view of the fact that the lubricator assembly must contain the well pressure while the equipment is inserted therein for subsequent utilization in the well, it is necessary to control the well pressure below the lubricator assembly during this procedure. This is achieved by the use of a valve assembly within the lubricator section. Some prior art lubricator risers contain normally "fail" open valve assemblies which permit the valve to automatically open if hydraulic control pressure is lost. Under certain conditions, if control pressure were lost, a blowout might result. Other lubricator valve assemblies contain normally "fail" closed valve assemblies which permit the valve to automatically close if hydraulic control pressure is lost. Normally "fail" closed valves can close and sever the wire or other line if control pressure is lost. There is, therefore, a possibility of damaging the valve and rendering it inoperable, thereby causing a blowout of the well.
Still other lubricator valve assemblies, such for example as shown in U.S. Pat. No. 4,062,406 to Akkerman et al, provide mechanical means for locking the valve manipulating mechanism when the valve element is in closed position.
It is recognized that any commercially practicable lubricator valve must provide means for reducing metallic friction on the ball valve surfaces during the opering and closing manipulating steps, as well as providing a metal to metal seal when excessive pressures must be resisted by the closed ball valve element.
A further desirable feature for any lubricator valve is the capability of pumping fluid, such as a kill fluid, around the valve when it is in a closed position, thus permitting the well to be brought under control without running the risk of opening the valve to supply the kill fluid.
It is desirable to be able to pressure test the well head when it has been closed and after introduction of a work or production string, prior to re-opening of the lubricator valve. With the present invention, the tubing can be tested between the well head connection and the lubricator with the lubricator valve in the closed position.
A last necessary function of a successful lubricator valve is the requirement that the tubing be pressured from the surface before re-opening the valve. Pressure above the tool must exceed pressure below the tool before it will open, thus assuring control of the well by a pressure source above the lubricator valve.